The DONAR ultrasonic system has demonstrated capability to detect and monitor continuously the changes in mineralization on the surface and in the subsurface of enamel blocks in vitro while the experiment is underway. Dissolution of layers can be followed with a resolution of 0.1 microns. This capability will be used to provide detailed information concerning the mineralization dynamics of intact enamel under a variety of conditions. It is intended to learn more about the development of subsurface demineralized zones, remineralization processes and the influence of the composition of the medium on these processes. It is of particular interest to investigate the fluoride effect in greater detail.